Optical sensor for odometry tracking to determine trajectory of a wheel

ABSTRACT

An optical sensor system for determining trajectory of a car, the optical sensor system being mounted in a wheel arch of the car, includes: a plurality of optical sensors mounted in the wheel arch above a wheel, the optical sensors being located behind a plurality of clear casings that do not touch the wheel, for performing a plurality of counts corresponding to respectively capturing a plurality of images of the wheel according to an outer surface of the wheel evenly covered with wheel treads. The captured images are compared with a reference image to determine a 2D displacement of the wheel from its original position. This measured 2D displacement is converted into a distance the wheel travels along a path, and the wheel trajectory is determined by calculating a turning degree of the wheel according to a trigonometric manipulation of the captured 2D displacement.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/930,668, which was filed on Nov. 3, 2015, thecontents of which are included herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to optical sensors, and more particularly,to an optical sensor which can be used to perform odometry tracking.

2. Description of the Prior Art

Optical sensors, such as those commonly used in a computer mouse, candetect miniscule changes in direction in order to track the motion of anobject over a 2D surface. Optical sensors work by illuminating thesurface on which the object moves to capture an image, and comparing areference image and the captured image in order to determine how farfrom the origin the object has moved. This image comparison generatesaccumulated delta y and delta x values; computer algorithms can then beused to determine the resultant motion of the object.

The advantage of optical sensors is that only a single sensor is neededto determine angular motion, as the optical sensor can generate bothdelta x and delta y values. Optical sensors are typically used inapplications where only small distances need to be determined, however.If an optical sensor could be implemented in an application which movesvia the use of wheels, the optical sensor could track the motion of thewheels and then convert the detected motion to real-life distance.

It is therefore an objective of the present invention to employ a singleoptical sensor for tracking motion of a wheel in order to performdistance and odometry tracking.

SUMMARY OF THE INVENTION

An optical sensor system for determining trajectory of a car, theoptical sensor system being mounted in a wheel arch of the car,comprises: a plurality of optical sensors mounted in the wheel archabove a wheel, the optical sensors being located behind a plurality ofclear casings that do not touch the wheel, for performing a plurality ofcounts corresponding to respectively capturing a plurality of images ofthe wheel according to an outer surface of the wheel evenly covered withwheel treads. The captured images are compared with a reference image todetermine a 2D displacement of the wheel from its original position.This measured 2D displacement is converted into a distance the wheeltravels along a path, and the wheel trajectory is determined bycalculating a turning degree of the wheel according to a trigonometricmanipulation of the captured 2D displacement.

A method for determining trajectory of a wheel comprises: utilizing afirst optical sensor mounted in the wheel arch above the wheel andbehind a first clear casing which does not touch the wheel, a secondoptical sensor mounted in the wheel arch on one side of the wheel andbehind a second clear casing which does not touch the wheel, and a thirdoptical sensor mounted in the wheel arch on the other side of the wheeland behind a third clear casing which does not touch the wheel toperform the steps of: capturing a plurality of images of the wheelaccording to evenly-spaced wheel treads on the outer surface of thewheel, to generate a plurality of counts, respectively; comparing thecaptured images with a reference image to determine a 2D displacement ofthe wheel; and performing a calculation to convert the measured 2Ddisplacement of the wheel from its original position into a distance thewheel travels along a path in order to determine the wheel trajectory.This calculation comprises: calculating a turning degree of the wheelaccording to a trigonometric manipulation of the captured 2Ddisplacement.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an optical sensor mounted above a wheel.

FIG. 2A is an illustration of accumulated motion generated by a wheelmoving in a straight direction.

FIG. 2B is an illustration of accumulated motion generated by a wheelmoving in an angular direction.

FIG. 3A is an illustration of generated angular motion of the wheelillustrated in FIG. 2.

FIG. 3B is an illustration of trajectory of the wheel illustrated inFIG. 2 being the front wheel of a car.

DETAILED DESCRIPTION

An exemplary embodiment of the present invention uses an optical sensorpositioned above a wheel, as illustrated in FIG. 1. The odometrytracking system 100 comprises a wheel 150 mounted in a wheel arch 120.Three optical sensors 131, 161 and 191 are illustrated in the diagram,being positioned at the top of the wheel arch, at the right side of thewheel arch and at the left side of the wheel arch, respectively. Eachoptical sensor is protected by a respective casing 133, 163, and 193.Signals generated by the optical sensors 131, 161 and 191, andpredetermined parameters of the odometry tracking system 100, are usedto perform calculations. It is noted that an exemplary embodiment of thepresent invention only requires a single optical sensor of theillustrated optical sensors 131, 161, 191 in order to perform odometrytracking. The three sensors are illustrated in order to give examples asto possible placement, but not to limit the invention.

The casings 133, 163, 193 are provided in order to protect therespective optical sensor 131, 161, 191 from damage. These casings canbe clear housings that are flush with the wheel arch 120 or protrude.The aim of the casings 133, 163, 193 is to protect the optical sensor131, 161, 191 from damage. Further, when the optical sensor 131, 161,191 is used to determine motion of a wheel in a car, the casing 133,163, 193 can also protect it from splashes etc.

By using one of the optical sensors 131, 161, 191, an accuratedetermination of how far the wheel 150 has travelled, as well as thetrajectory of the wheel 150, can be estimated. As detailed above, theoptical sensors 131, 161, 191 are mounted on the top of the wheel arch120. The wheel arch 120 could be a wheel arch of a motorized vehiclesuch as a car, or a wheel arch in a treadmill. As the wheel 150 rotates,the optical sensors 131, 161, 191 generate reports based on a number oftreads which are imaged.

Refer to FIG. 2A and FIG. 2B, which illustrate how the reports/counts ofthe optical sensor generate accumulated motion parameters. FIG. 2Aillustrates the generated accumulated motion when the wheel 150 rotateswithout turning. As shown in the diagram, no x values are generated buty values are generated in the opposite direction from the wheel motion.These accumulated values can be termed Dy.

FIG. 2B illustrates the generated accumulated motion when the wheel 150rotates and turns at the same time. As shown in the diagram, both x andy values are generated in the opposite direction from the wheel motion.In order to determine the resultant distance of the wheel 150, thehypotenuse of Dx and Dy must be calculated. This value can then betranslated into a real-world distance.

A calibration step generates a ratio that can be used for conversion.The calibration process is performed to calculate how far the wheelturns for each count of the sensor. As noted above, the countcorresponds to a sensor tread of the sensor. Assuming the wheel rotatesas illustrated in FIG. 2A, then it can be calculated how far in realterms the wheel turns because the circumference, C, of the wheel is aknown value.

The circumference of the wheel can be calculated using the Pythagoreanequation: C=2πr

As the wheel rotates, delta y values are accumulated until Dycorresponds to one rotation of the wheel. The accumulated value Dy has adirect relationship to C. It is determined how many reports/counts thereare in Dy, and this value is used to divide the circumference C in orderto generate a distance per count (dpc). This is illustrated by thefollowing equation:

$\begin{matrix}{{dpc} = {\frac{C}{Dy} = \frac{2\pi \; r}{Dy}}} & (1)\end{matrix}$

A trajectory of the wheel 150 is then determined. If the optical sensor131, 161, 191 only plots a change in the y direction, i.e. only delta yvalues are generated, then the wheel 150 is determined to be rotatingwithout turning and a simple conversion of counts can be used togenerate the distance travelled by the wheel 150. If, however, the wheel150 is both turning and rotating then the angle θ of the wheel turn canbe calculated using simple trigonometry, as illustrated in FIG. 3A andshown by the following equation:

$\begin{matrix}{{\tan \mspace{14mu} \theta} = \frac{Dx}{Dy}} & (2)\end{matrix}$

Once the turning angle of the wheel 150 is determined, a trajectory ofthe wheel 150 can be plotted, as illustrated in FIG. 3B. FIG. 3B is adiagram of the odometry system 100 being a car with four wheels. Thefront right-hand wheel is the wheel 150 illustrated in FIG. 3B. As theturning angle θ of the wheel 150 is known, the internal angle betweenthe wheel and the side of the car can be calculated by using rightangles i.e. 90°−θ.

A perpendicular line to the turned wheel 150 will intersect with anextended line from the rear axles of the car 100 to form a right-angledtriangle having sides L, R and E. L is the length of the car 100 andtherefore is a known value. Using trigonometry, the length of R and Ecan be calculated, as illustrated by the following equations:

$\begin{matrix}{R = \frac{L}{\sin \mspace{14mu} \theta}} & (3) \\{E = \frac{L}{\cos \mspace{14mu} \theta}} & (4)\end{matrix}$

As illustrated by the dotted lines, the car 100 will move along a curvehaving a radius R from point O. By using the optical sensor 131, 161,191 to determine a rotated distance of the wheel 150 and converting thatdistance into real-world values, a total distance d moved along thecurve by the car 100 can be calculated.

As detailed above, a distance per count has been calculated in thecalibration stage. This value can be used to calculate a real distancetaken by the vehicle 100. When the vehicle 100 moves in a straightdirection i.e. no change in x, the values can be directly put intoequation (1) by multiplying a number of counts (treads) with thedistance per count. In effect, this converts a distance monitored by theoptical sensor 131, 161, 191 into a real distance. This is shown belowas equation (5):

Distance=Dy×dpc

If the vehicle 100 is turning, the displacement measured by the opticalsensor 131, 161, 191 is calculated number by using the hypotenuse of Dxand Dy. This value is then converted into counts, and is multiplied withthe value dpc to determine a distance travelled along the curve. This isshown below as equation (6):

Distance=√{square root over (Dx ² +Dy ²)}×dpc

The final stage in the calculation places this determined distance onthe curve calculated in FIG. 3B. In this way, a trajectory of a wheelcan be calculated to high accuracy.

Although the above is described using a car as an exemplary embodiment,it should be appreciated that the concept can be applied to anyapplication which tracks the motion of a wheel. Further, the opticalsensor can also be calibrated to determine a vertical distance from thewheel, so that if air pressure of the wheel changes or some otherfactors cause the distance between the optical sensor and the wheel tochange (the vehicle moves over rocky terrain, for example) the change indistance can be compensated for.

No matter what implementation the optical sensor is applied to, thewheel radius should be set as a known parameter in an initializationprocedure. In the example provided in FIG. 3B, the length of the car Land the distance between the rear axles W will be known values and canalso be set as the initialization parameters. This is not a limitationof the invention.

To summarize, the present invention provides an optical sensor which canutilize changes in 2D motion of a wheel to determine angular motion ofthe wheel. By plotting a trajectory of the wheel using the determinedchange in motion, a distance the wheel moves along said trajectory canalso be determined.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. An optical sensor system for determiningtrajectory of a car, the optical sensor system being mounted in a wheelarch of the car, and comprising: a first optical sensor mounted in thewheel arch above a wheel, an outer surface of the wheel being coveredwith evenly-spaced wheel treads, wherein the first optical sensor islocated behind a first clear casing that does not touch the wheel, andthe first optical sensor performs a plurality of counts corresponding torespectively capturing a plurality of images of the wheel according tothe wheel treads; a second optical sensor mounted in the wheel arch onone side of the wheel, wherein the second optical sensor is locatedbehind a second clear casing that does not touch the wheel, and thesecond optical sensor performs a plurality of counts corresponding torespectively capturing a plurality of images of the wheel according tothe wheel treads; and a third optical sensor mounted in the wheel archon the other side of the wheel, wherein the third optical sensor islocated behind a third clear casing that does not touch the wheel, andthe third optical sensor performs a plurality of counts corresponding torespectively capturing a plurality of images of the wheel according tothe wheel treads; wherein the captured images of at least one of theoptical sensors is compared with a reference image to determine a 2Ddisplacement of the wheel from its original position, this measured 2Ddisplacement is converted into a distance the wheel travels along apath, and the wheel trajectory is determined by calculating a turningdegree of the wheel according to a trigonometric manipulation of thecaptured 2D displacement.
 2. The optical sensor system of claim 1,wherein the calculated turning degree and at least a distance between afront wheel axle and a rear wheel axle of the car are utilized todetermine a turning curve along which the wheel moves, wherein theturning curve is centered on a point where an extended line from therear axle crosses a perpendicular line to the front axle.
 3. The opticalsensor system of claim 1, wherein a calibration process is performedwhen the wheel rotates but does not turn, the calibration processcomprising: measuring a 2D displacement of the wheel corresponding to asingle rotation of the wheel; determining how many counts are performedaccording to this single rotation; and utilizing a circumference of thewheel to determine a distance per count (dpc) value, wherein the dpcvalue is used to convert the measured 2D displacement into a distancethe wheel travels along a path.
 4. A method for using an optical sensorsystem mounted in a wheel arch of a car to determine trajectory of thecar, the method comprising: utilizing a first optical sensor mounted inthe wheel arch above the wheel and behind a first clear casing whichdoes not touch the wheel, a second optical sensor mounted in the wheelarch on one side of the wheel and behind a second clear casing whichdoes not touch the wheel, and a third optical sensor mounted in thewheel arch on the other side of the wheel and behind a third clearcasing which does not touch the wheel to perform the following steps:capturing a plurality of images of the wheel according to evenly-spacedwheel treads on an outer surface of the wheel, to generate a pluralityof counts, respectively; comparing the captured images of at least oneof the optical sensors with a reference image to determine a 2Ddisplacement of the wheel; and performing a calculation to convert themeasured 2D displacement of the wheel from its original position into adistance the wheel travels along a path in order to determine the wheeltrajectory, comprising: calculating a turning degree of the wheelaccording to a trigonometric manipulation of the captured 2Ddisplacement.
 5. The method of claim 4, wherein the step of performing acalculation to determine the wheel trajectory further comprises:utilizing the calculated turning degree and at least a distance betweena front wheel axle and a rear wheel axle of the car to determine aturning curve along which the wheel moves, the turning curve beingcentered on a point where an extended line from the rear axle crosses aperpendicular line to the front axle.
 6. The method of claim 4, whereina calibration process is performed when the wheel rotates but does notturn, the calibration process comprising the following steps: measuringa 2D displacement of the wheel corresponding to a single rotation of thewheel; determining how many counts are performed according to thissingle rotation; and utilizing a circumference of the wheel to determinea distance per count (dpc) value; wherein the dpc value is used toconvert the measured 2D displacement into a distance the wheel travelsalong a path.